KR20140095652A - Electrolyte for lithium rechargeable battery and lithium rechargeable battery including the electrolyte - Google Patents

Abstract

The present invention relates to an electrolyte for a rechargeable lithium battery including an ionic liquid represented by the chemical formula 1, a lithium salt, and an organic solvent, and a rechargeable lithium battery including the electrolyte for a rechargeable lithium battery. The electrolyte ensures battery stability due to resolved flame retardancy and prevents deterioration of battery performance by adjusting viscosity of an electrolyte.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an electrolyte for a lithium secondary battery, and a lithium secondary battery comprising the same. BACKGROUND ART < RTI ID = 0.0 >

To an electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same.

A battery is a device that converts the chemical energy generated by an electrochemical oxidation-reduction reaction of an internal chemical substance into electrical energy. When the energy inside the battery is exhausted, the primary battery and the rechargeable secondary battery . Among them, the secondary battery can be used by charging and discharging several times by using reversible conversion between chemical energy and electric energy.

On the other hand, the development of high-tech electronic industry has made it possible to miniaturize and lighten electronic equipment, and the use of portable electronic devices is increasing. The need for a battery having a high energy density as a power source for such portable electronic devices has been increased, and research on lithium secondary batteries has been actively conducted.

The lithium secondary battery includes a positive electrode including a positive electrode active material capable of intercalating and deintercalating lithium, a negative electrode including a negative active material capable of intercalating and deintercalating lithium, And the electrolyte solution is injected into the battery cell.

The electrolytic solution uses an organic solvent in which a lithium salt is dissolved and is important for determining the stability and performance of the lithium secondary battery.

One embodiment provides an electrolyte solution for a lithium secondary battery capable of improving performance while ensuring stability.

Another embodiment provides a lithium secondary battery comprising the electrolytic solution.

According to one embodiment, there is provided an electrolyte solution for a lithium secondary battery comprising an ionic liquid represented by the following formula (1), a lithium salt, and an organic solvent:

[Chemical Formula 1]

In Formula 1,

R ¹ is selected from the group consisting of hydrogen, a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstituted C6 to C30 aryl group, a substituted or unsubstituted C1 to C20 heteroalkyl group, An unsubstituted C2 to C30 heterocycloalkyl group, a substituted or unsubstituted C2 to C30 heteroaryl group, or a combination thereof,

R ² is a substituted or unsubstituted C1 to C30 alkoxy group,

R ³ and R ⁴ are each independently hydrogen, a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstituted C6 to C30 aryl group, C20 heteroalkyl group, a substituted or unsubstituted C2 to C30 heterocycloalkyl group, a substituted or unsubstituted C2 to C30 heteroaryl group, or a combination thereof,

L is a single bond or a substituted or unsubstituted C1 to C20 alkylene group,

X ¹ to X ⁶ are each independently a halogen atom, a C1 to C20 alkyl group substituted with at least one halogen atom, a C1 to C20 cycloalkyl group substituted with at least one halogen atom, a C1 to C20 aryl group substituted with at least one halogen atom, A combination thereof,

At least two of X ¹ to X ⁶ are each independently a C1 to C20 alkyl group substituted with at least one halogen atom, a C1 to C20 cycloalkyl group substituted with at least one halogen atom, a C1 to C20 aryl group substituted with at least one halogen atom Or a combination thereof.

The ionic liquid may be represented by the following formula (2).

(2)

In Formula 2,

R ¹ is selected from the group consisting of hydrogen, a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstituted C6 to C30 aryl group, a substituted or unsubstituted C1 to C20 heteroalkyl group, An unsubstituted C2 to C30 heterocycloalkyl group, a substituted or unsubstituted C2 to C30 heteroaryl group, or a combination thereof,

R ² is a substituted or unsubstituted C1 to C30 alkoxy group,

R ³ and R ⁴ are each independently hydrogen, a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstituted C6 to C30 aryl group, C20 heteroalkyl group, a substituted or unsubstituted C2 to C30 heterocycloalkyl group, a substituted or unsubstituted C2 to C30 heteroaryl group, or a combination thereof,

L is a single bond or a substituted or unsubstituted C1 to C20 alkylene group.

The ionic liquid may be represented by the following formula (3).

(3)

The ionic liquid may be contained in an amount of about 1% by volume to 50% by volume based on the total amount of the electrolytic solution.

The ionic liquid may be included in an amount of about 5% by volume to 40% by volume based on the total amount of the electrolytic solution.

The electrolytic solution may further contain a carbonate compound substituted with fluorine.

The fluorine-substituted carbonate-based compound may include fluoroethylene carbonate (FEC).

The fluorine-substituted carbonate compound may be contained in an amount of about 1 to 40% by weight based on the total amount of the electrolytic solution.

The organic solvent may include EC / EMC / DMC.

The electrolyte may have a viscosity of about 100 cP or less.

The electrolyte may have a viscosity of about 3 to 100 cP.

The electrolyte may have a viscosity of about 3 to 15 cP.

The electrolyte may have an ion conductivity of about 1.0 x 10 ^-3 to 9.9 x 10 ^-3 S / cm.

According to another embodiment, there is provided a positive electrode comprising a positive electrode active material, a negative electrode including a negative electrode active material, and a lithium secondary battery including the electrolyte solution.

The lithium secondary battery may further include a passivation film formed on a surface of the cathode, and the passivation film may be formed from the electrolyte solution.

It is possible to improve the flame retardancy and ensure the stability of the battery while maintaining the viscosity of the electrolyte appropriately to prevent deterioration of the performance of the battery.

1 is a schematic view showing a lithium secondary battery according to one embodiment.

Hereinafter, exemplary embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Unless otherwise defined herein, 'substituted' means that a hydrogen atom in the compound is a halogen atom (F, Br, Cl or I), a hydroxy group, an alkoxy group, a nitro group, a cyano group, an amino group, A carboxyl group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid or a salt thereof, a C1 to C20 alkyl group, a C2 to C20 alkenyl group, a C2 to C20 alkenyl group, a C2 to C20 alkenyl group, C6 to C30 aryl groups, C7 to C30 arylalkyl groups, C1 to C20 alkoxy groups, C1 to C20 heteroalkyl groups, C3 to C20 heteroarylalkyl groups, C3 to C30 cycloalkyl groups, C3 to C15 cycloalkenyl groups, C6 to C20 aryl groups, C15 cycloalkynyl group, a C2 to C20 heterocycloalkyl group, and combinations thereof.

In addition, unless otherwise defined herein, "hetero" means containing 1 to 3 heteroatoms selected from N, O, S and P.

Hereinafter, an electrolyte solution for a lithium secondary battery according to one embodiment will be described.

An electrolyte for a lithium secondary battery according to an embodiment includes an ionic liquid represented by the following formula (1), a lithium salt, and an organic solvent.

[Chemical Formula 1]

In Formula 1,

R ¹ is selected from the group consisting of hydrogen, a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstituted C6 to C30 aryl group, a substituted or unsubstituted C1 to C20 heteroalkyl group, An unsubstituted C2 to C30 heterocycloalkyl group, a substituted or unsubstituted C2 to C30 heteroaryl group, or a combination thereof,

R ² is a substituted or unsubstituted C1 to C30 alkoxy group,

R ³ and R ⁴ are each independently hydrogen, a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstituted C6 to C30 aryl group, C20 heteroalkyl group, a substituted or unsubstituted C2 to C30 heterocycloalkyl group, a substituted or unsubstituted C2 to C30 heteroaryl group, or a combination thereof,

L is a single bond or a substituted or unsubstituted C1 to C20 alkylene group,

X ¹ to X ⁶ are each independently a halogen atom, a C1 to C20 alkyl group substituted with at least one halogen atom, a C1 to C20 cycloalkyl group substituted with at least one halogen atom, a C1 to C20 aryl group substituted with at least one halogen atom, A combination thereof,

At least two of X ¹ to X ⁶ are each independently a C1 to C20 alkyl group substituted with at least one halogen atom, a C1 to C20 cycloalkyl group substituted with at least one halogen atom, a C1 to C20 aryl group substituted with at least one halogen atom Or a combination thereof.

The compound represented by Formula 1 is an ionic liquid containing cations and anions, and is a salt that exhibits liquid characteristics at room temperature.

In general, an ionic liquid is contained in an electrolytic solution to improve the flame retardancy. However, when the ionic liquid is excessively contained in order to improve the flame retardancy, the viscosity of the electrolyte increases, which may affect the performance and lifetime of the lithium secondary battery.

The electrolytic solution according to this embodiment includes the compound represented by Formula 1 as an ionic liquid, thereby improving the flame retardancy and preventing the viscosity of the electrolytic solution from increasing.

Specifically, the compound represented by Formula 1 includes a cation containing pyrrolidinium substituted with an alkoxy group-containing group and a bulky anion.

The pyrrolidinium substituted with the alkoxy group-containing group can be decomposed in the alkoxy group portion to form a passivation film on the electrode. The passivation film lowers the exothermic characteristic to improve the flame retardancy and improve the performance of the lithium secondary battery can do.

The anion has a bulky portion, for example, at least two of X ¹ to X ⁶ has a hydrocarbon moiety substituted with a halogen atom, thereby preventing the viscosity of the electrolyte from increasing.

Therefore, the compound represented by the above formula (1) improves the flame retardancy and improves the stability of the battery and maintains the viscosity of the electrolyte appropriately, thereby preventing the performance and life characteristics of the lithium secondary battery from becoming poor.

The ionic liquid may be, for example, a compound represented by the following formula (2).

(2)

In Formula 2, R ¹ to R ⁴ and L are as defined above.

The ionic liquid may be, for example, a compound represented by the following formula (3).

(3)

The ionic liquid may be included in an amount of about 1% by volume to about 50% by volume based on the total amount of the electrolytic solution. By being included in the above range, the flame retardancy can be improved while maintaining the viscosity of the electrolytic solution appropriately. From about 5% by volume to about 40% by volume within the above range.

The organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

As the organic solvent, a carbonate, ester, ether, ketone, alcohol, or aprotic solvent may be used.

Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC) EC), propylene carbonate (PC), and butylene carbonate (BC). The carbonate-based solvent may be, for example, a mixture of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) at a predetermined ratio.

Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethylacetate, methyl propionate, ethyl propionate, gamma-butyrolactone, decanolide, gamma-valerolactone, Mevalonolactone, caprolactone, etc. may be used.

Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran. As the ketone solvent, cyclohexanone may be used have. As the alcoholic solvent, ethyl alcohol, isopropyl alcohol and the like can be used. As the aprotic solvent, R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group , A double bond aromatic ring or an ether bond); Amides such as dimethylformamide or dimethylacetamide, dioxolanes such as 1,3-dioxolane, and sulfolanes.

The organic solvent may be used singly or in a mixture of one or more. If one or more of the organic solvents are used in combination, the mixing ratio may be appropriately adjusted according to the performance of the desired battery, and this may be widely understood by those skilled in the art have.

In the case of the carbonate-based solvent, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1: 1 to about 1: 9, the performance of the electrolytic solution may be excellent.

The organic solvent may further include an aromatic hydrocarbon-based organic solvent in the carbonate-based solvent. At this time, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of about 1: 1 to about 30: 1.

Specific examples of the aromatic hydrocarbon-based organic solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-tri Fluorobenzene, 1,2,4-trifluorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1 , 2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, Examples of the solvent include 2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4- Dichlorotoluene, 2,3-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2, 3-dichlorotoluene, 3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2 , 5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and combinations thereof.

The lithium salt is dissolved in the non-aqueous organic solvent to act as a source of lithium ions in the battery to enable operation of a basic lithium secondary battery, and a material capable of promoting the movement of lithium ions between the positive electrode and the negative electrode to be. The lithium salt Representative examples are _{LiPF 6, LiBF 4, LiSbF 6} , LiAsF 6, LiN (SO 2 C 2 F 5) 2, Li (CF 3 SO 2) 2 N, LiN (SO 3 C 2 F 5) 2, _{LiC 4 F 9 SO 3, LiClO} 4, LiAlO 2, LiAlCl 4, LiN (C x F 2x +1 SO 2) (C y F 2y +1 SO 2) ( where, x and y are natural numbers), LiCl, and LiI. ≪ / RTI >

The concentration of the lithium salt can be used within the range of about 0.1M to about 2.0M. When the concentration of the lithium salt is within the above range, the electrolytic solution has an appropriate conductivity and viscosity, so that it can exhibit excellent electrolyte performance, and lithium ions can effectively move.

The electrolytic solution may further include an additive. The additive may be, for example, a carbonate compound substituted with fluorine, for example, fluoroethylene carbonate (FEC).

The fluorine-substituted carbonate compound may be contained in an amount of about 1 to 40% by weight based on the total amount of the electrolytic solution. By including it in the above-described range, it is possible to prevent the viscosity of the electrolytic solution from increasing sharply while forming the passivation film on the electrode surface with an appropriate thickness.

The electrolyte may have a viscosity of, for example, about 100 cP or less and a viscosity of about 3 cP to 100 cP. By having the viscosity within the above range, the cycle characteristics of the lithium secondary battery are not deteriorated and the lifetime characteristics can be improved. And may have a viscosity within the range of about 3 to 15 cP.

The electrolyte may have an ionic conductivity of, for example, about 1.0 x 10 ^-3 to 9.9 x 10 ^-3 S / cm. By having the ion conductivity in the above range, the performance of the battery to which the electrolyte is applied can be improved.

Hereinafter, a lithium secondary battery according to another embodiment will be described with reference to FIG.

1 is a schematic view showing a lithium secondary battery according to one embodiment.

1, a lithium secondary battery 100 according to an embodiment includes a cathode 112, a cathode 114 positioned opposite the cathode 112, and a cathode 112 disposed between the cathode 112 and the anode 114 (Not shown) for impregnating the negative electrode 112, the positive electrode 114 and the separator 113, and a battery cell 120 containing the battery cell And a sealing member 140 that seals the battery container 120.

The lithium secondary battery 100 may be manufactured by stacking a cathode 112, a separator 113 and an anode 114 in this order and then winding the battery in a spiral wound state in the battery container 120.

The cathode 112 includes a current collector and a negative electrode active material layer formed on the current collector.

The current collector may be a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foil, a copper foil, a polymer substrate coated with a conductive metal, or a combination thereof.

The negative electrode active material layer includes a negative electrode active material, a binder, and optionally a conductive material.

The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, a lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

As a material capable of reversibly intercalating / deintercalating lithium ions, any carbonaceous anode active material commonly used in lithium ion secondary batteries can be used as the carbonaceous material. Typical examples thereof include crystalline carbon , Amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in the form of amorphous, plate-like, flake, spherical or fibrous type. Examples of the amorphous carbon include soft carbon (soft carbon) Or hard carbon, mesophase pitch carbide, fired coke, and the like.

Examples of the lithium metal alloy include lithium and a metal such as Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Alloys may be used.

As the material capable of doping and dedoping lithium, Si, SiO _x (0 <x <2), Si-C composite, Si-Q alloy (Q is an alkali metal, an alkaline earth metal, A transition metal, a rare earth element or a combination thereof and not Si), Sn, SnO ₂ , Sn-C composite, Sn-R (wherein R is an alkali metal, an alkaline earth metal, A rare earth element or a combination thereof, but not Sn). The specific elements of Q and R include Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Sb, Bi, S, Se, Te, Po, or a combination thereof.

Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide, and the like.

The binder serves to adhere the anode active material particles to each other and to adhere the anode active material to the current collector. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, Such as polyvinyl chloride, polyvinyl fluoride, polymers comprising ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, Styrene-butadiene rubber, epoxy resin, nylon, and the like may be used, but the present invention is not limited thereto.

The conductive material is used for imparting conductivity to the electrode. Any material can be used as long as it does not cause any chemical change in the battery. Examples of the conductive material include natural graphite, artificial graphite, carbon black, acetylene black, , Carbon-based materials such as carbon fibers; Metal powders such as copper, nickel, aluminum, and silver, or metal-based materials such as metal fibers; Conductive polymers such as polyphenylene derivatives; Or a mixture thereof may be used.

The anode 114 includes a current collector and a cathode active material layer formed on the current collector.

Al may be used as the current collector, but the present invention is not limited thereto.

The cathode active material layer includes a cathode active material, a binder, and optionally a conductive material.

As the cathode active material, a compound capable of reversibly intercalating and deintercalating lithium (a lithiated intercalation compound) can be used. Concretely, it is possible to use at least one of complex oxides of cobalt, manganese, nickel or a combination of metals and lithium, and specific examples thereof include compounds represented by any one of the following formulas. Li _a A _{1 - b} R _b D ₂ wherein, in the formula, 0.90? A? 1.8 and 0? B? 0.5; Li _a E _{1 - b} R _b O _{2 - c} D _c , wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05; LiE _{2 - b} R _b O _{4 - c} D _{c where} 0? B? 0.5, 0? C? 0.05; Li _a Ni _{1 -b- c} Co _b R _c D _{α where} 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α ≦ 2; Li _a Ni _{1 - b - c} Co _b R _c O _{2 - ?} Z _{? Wherein} 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _{1 -b- c} Co _b R _c O _{2 - ?} Z ₂ wherein 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, and 0 <? Li _a Ni _1-bc Mn _b R _c D _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _{1 -b- c} Mn _b R _c O _{2 - ?} Z _{? Where the} 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _{1 -b- c} Mn _b R _c O _{2 - ?} Z ₂ wherein 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _b E _c G _d O ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, and 0.001 ≤ d ≤ 0.1; Li _a Ni _b Co _c Mn _d G _e O ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, and 0.001 ≤ e ≤ 0.1; Li _a NiG _b O ₂ (in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1); Li _a CoG _b O ₂ (in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1); Li _a MnG _b O ₂ wherein, in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1; Li _a Mn ₂ G _b O ₄ (in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1); QO _2; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiTO ₂ ; LiNiVO _4; Li _(3-f) J ₂ (PO ₄ ) ₃ (0? F? 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0? F? 2); And LiFePO _4.

In the above formula, A is Ni, Co, Mn or a combination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P or a combination thereof; E is Co, Mn or a combination thereof; Z is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; T is Cr, V, Fe, Sc, Y or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

Of course, a compound having a coating layer on the surface of the compound may be used, or a compound having a coating layer may be mixed with the compound. The coating layer may comprise, as a coating element compound, an oxide, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, or a hydroxycarbonate of a coating element. The compound constituting these coating layers may be amorphous or crystalline. The coating layer may contain Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or a mixture thereof. The coating layer forming step may be carried out by any of coating methods such as spray coating, dipping, and the like without adversely affecting the physical properties of the cathode active material by using these elements in the above compound. It is a content that can be well understood by people engaged in the field, so detailed explanation will be omitted.

The binder serves to adhere the positive electrode active material particles to each other and to adhere the positive electrode active material to the current collector. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl Polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-acrylonitrile, styrene-butadiene rubber, Butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like, but not limited thereto.

The conductive material is used for imparting conductivity to the electrode. Any conductive material can be used without causing any chemical change in the battery. Examples of the conductive material include natural graphite, artificial graphite, carbon black, acetylene black, Metal powders such as black, carbon fiber, copper, nickel, aluminum, and silver, metal fibers, and the like, and conductive materials such as polyphenylene derivatives may be used alone or in combination.

The negative electrode and the positive electrode may be prepared by preparing an active material composition by mixing an active material, a binder and, optionally, a conductive material in a solvent, and applying the active material composition to each current collector. As the solvent, N-methylpyrrolidone or the like can be used, but it is not limited thereto. The method of manufacturing the electrode is well known in the art, and therefore, a detailed description thereof will be omitted herein.

The separator 113 separates the cathode 112 and the anode 114 and provides a passage for lithium ions. Any separator 113 may be used as long as it is commonly used in a lithium battery. That is, it is possible to use an electrolyte having a low resistance to ion movement and an excellent ability to impregnate an electrolyte. For example, selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be nonwoven fabric or woven fabric. For example, a polyolefin-based polymer separator such as polyethylene, polypropylene and the like is mainly used for a lithium ion battery, and a coated separator containing a ceramic component or a polymer substance may be used for heat resistance or mechanical strength, Structure.

The lithium secondary battery can be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery according to the type of the separator and electrolyte used. The lithium secondary battery can be classified into a cylindrical shape, a square shape, a coin shape, Depending on the size, it can be divided into bulk type and thin type. The structure and the manufacturing method of these cells are well known in the art, and detailed description thereof will be omitted.

The electrolytic solution is as described above.

Hereinafter, the aspects of the present invention described above will be described in more detail through examples. However, the following examples are for illustrative purposes only and do not limit the scope of the invention.

Preparation of electrolytic solution

Example  One

1.3 M LiPF ₆ lithium salt was added to a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) at a ratio of 3/4/3 (v / v / v) , And 20% by volume of an ionic liquid represented by the following Formula 3 was added to 80 vol% of the mixture to prepare an electrolyte for a lithium secondary battery.

 (3)

Example  2

An electrolyte solution for a lithium secondary battery was prepared in the same manner as in Example 1 except that 5% by weight of fluoroethylene carbonate (FEC) was further added.

Comparative Example  One

An electrolyte solution for a lithium secondary battery was prepared in the same manner as in Example 1, except that the ionic liquid was not included.

Comparative Example  2

An electrolyte solution for a lithium secondary battery was prepared in the same manner as in Example 1, except that the ionic liquid represented by the following Formula (A) was used instead of the ionic liquid represented by the Formula (3).

(A)

Evaluation 1: Evaluation of flammability

The flame retardancy of the electrolytic solution according to Examples 1 and 2 and Comparative Example 1 was evaluated.

The flame retardancy was evaluated by a glass fiber filter (1 cm x 1 cm) impregnated with the electrolytic solution according to Examples 1 and 2 and Comparative Example 1 for 30 seconds, followed by firing the glass fiber filter for 2 seconds to 4 seconds . The time can be expressed as a self-extinguishing time (SET), expressed in hours per unit weight (sec / g).

The results are shown in Table 1.

SET (sec / g) Example 1 25 Example 2 14 Comparative Example 1 60

Referring to Table 1, it can be seen that the electrolytic solution according to Examples 1 and 2 has a shorter spontaneous extinguishing time than the electrolytic solution according to Comparative Example 1. From this, it can be confirmed that the electrolytic solution according to Examples 1 and 2 has better flame retardancy than the electrolytic solution according to Comparative Example 1.

Evaluation 2: Viscosity evaluation

The viscosities of electrolytes according to Examples 1 and 2 and Comparative Example 2 were evaluated.

The viscosity was evaluated using a Brookfield viscometer (model: LVDV-II + PCP).

The results are shown in Table 2.

Viscosity (cP) Example 1 8.4 Example 2 10.2 Comparative Example 2 18.0

Referring to Table 2, it can be seen that the electrolytic solution according to Examples 1 and 2 has a lower viscosity than the electrolytic solution according to Comparative Example 2.

Evaluation 3: Evaluation of ionic conductivity

The ionic conductivities of electrolytes according to Examples 1 and 2 and Comparative Examples 1 and 2 were evaluated.

Ion conductivity measurements were made using a Mettler Toledo S30 SevenEasy Conductivity instrument.

The results are shown in Table 3.

Ion conductivity (S / cm) Example 1 5.2 x 10 ^-3 Example 2 3.9 x 10 ^-3 Comparative Example 2 1.1 x 10 ^-4

Referring to Table 3, it can be seen that the electrolytic solution according to Examples 1 and 2 has improved ionic conductivity than the electrolytic solution according to Comparative Example 2. [

Rating 4: Charging and discharging  Character rating

A lithium secondary battery was produced using electrolytes according to Examples 1 and 2 and Comparative Examples 1 and 2. At this time, the anode is _{LiNi 0 .5 Co 0 .2 Mn 0} .3 O 2 92 % by weight of Denka black (Denka black) 4% by weight of polyvinylidene fluoride (PVdF, Solef6020) 4 was used as a% by weight, An artificial graphite (ICG 10H) cathode was used as the cathode.

The charge / discharge characteristics of the lithium secondary battery using the electrolytic solution according to Examples 1 and 2 and Comparative Examples 1 and 2 were evaluated.

Charge and discharge were performed at 0.1 C, 0.1 V charge potential (0.02 C cut-off) and 0.1 C, 1.0 V discharge potential in the first cycle and 0.2 C, 0.1 V charge potential (0.05 C cut- Charging and discharging were carried out at 0.2C and 1.0V discharging potential and 0.5C, 0.1V charging potential (0.05C cut-off) and 0.5C, 1.0V discharging potential in the third cycle, and 1C (0.05C cut-off) and 1C, 1.0V discharging potential in the fifth cycle, and 2C, 0.1V charging potential (0.05C cut-off) and 2C, 1.0V discharging potential Were charged and discharged.

Table 4 shows the discharge capacity, charge capacity and irreversible efficiency of charge and discharge obtained from the above.

0.5 C charge / discharge capacity (mAh / g) 2C Charging / discharging capacity (mAh / g) ICE (%)
(Initial Columbic Efficiency) Charging capacity
(@ 0.5C) Discharge capacity
(@ 0.5C) Charging capacity
(@ 2C) Discharge capacity
(@ 2C) Example 1 327 331 159 248 90.3 Example 2 347 350 263 337 93.9 Comparative Example 1 344 345 302 330 95.2 Comparative Example 2 280 285 N / A N / A 85.0

Referring to Table 4, it can be seen that the lithium secondary battery using the electrolytic solution according to Examples 1 and 2 exhibits a capacity characteristic similar to that of Comparative Example 1 and exhibits improved capacity characteristics compared with Comparative Example 2.

In summary, the results of Tables 1 to 4 indicate that when the electrolytic solution according to Examples 1 and 2 is used, the flame retardancy is improved and the battery characteristics can be improved as compared with the case of using the electrolytic solution according to Comparative Examples 1 and 2 Able to know.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, And falls within the scope of the invention.

100: Lithium secondary battery
112: cathode
113: Separator
114: anode
120: Battery container
140: sealing member

Claims (15)

An ionic liquid represented by the following formula (1)
Lithium salt, and
Organic solvent
An electrolyte solution for a lithium secondary battery comprising:
[Chemical Formula 1]

In Formula 1,
R ¹ is selected from the group consisting of hydrogen, a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstituted C6 to C30 aryl group, a substituted or unsubstituted C1 to C20 heteroalkyl group, An unsubstituted C2 to C30 heterocycloalkyl group, a substituted or unsubstituted C2 to C30 heteroaryl group, or a combination thereof,
R ² is a substituted or unsubstituted C1 to C30 alkoxy group,
R ³ and R ⁴ are each independently hydrogen, a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstituted C6 to C30 aryl group, C20 heteroalkyl group, a substituted or unsubstituted C2 to C30 heterocycloalkyl group, a substituted or unsubstituted C2 to C30 heteroaryl group, or a combination thereof,
L is a single bond or a substituted or unsubstituted C1 to C20 alkylene group,
X ¹ to X ⁶ are each independently a halogen atom, a C1 to C20 alkyl group substituted with at least one halogen atom, a C1 to C20 cycloalkyl group substituted with at least one halogen atom, a C1 to C20 aryl group substituted with at least one halogen atom, A combination thereof,
At least two of X ¹ to X ⁶ are each independently a C1 to C20 alkyl group substituted with at least one halogen atom, a C1 to C20 cycloalkyl group substituted with at least one halogen atom, a C1 to C20 aryl group substituted with at least one halogen atom Or a combination thereof
Electrolyte for lithium secondary battery.
The method of claim 1,
Wherein the ionic liquid is represented by the following Formula 2:
(2)

In Formula 2,
R ¹ is selected from the group consisting of hydrogen, a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstituted C6 to C30 aryl group, a substituted or unsubstituted C1 to C20 heteroalkyl group, An unsubstituted C2 to C30 heterocycloalkyl group, a substituted or unsubstituted C2 to C30 heteroaryl group, or a combination thereof,
R ² is a substituted or unsubstituted C1 to C30 alkoxy group,
R ³ and R ⁴ are each independently hydrogen, a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstituted C6 to C30 aryl group, C20 heteroalkyl group, a substituted or unsubstituted C2 to C30 heterocycloalkyl group, a substituted or unsubstituted C2 to C30 heteroaryl group, or a combination thereof,
L is a single bond or a substituted or unsubstituted C1 to C20 alkylene group.
3. The method of claim 2,
Wherein the ionic liquid is represented by the following Formula 3:
(3)

The method of claim 1,
Wherein the ionic liquid is contained in an amount of 1% by volume to 50% by volume based on the total amount of the electrolytic solution.
5. The method of claim 4,
Wherein the ionic liquid is contained in an amount of 5% by volume to 40% by volume based on the total amount of the electrolytic solution.
The method of claim 1,
The electrolyte solution for a lithium secondary battery further comprising a carbonate compound substituted with fluorine.
The method of claim 6,
Wherein the fluorine-substituted carbonate compound comprises fluoroethylene carbonate (FEC).
The method of claim 6,
Wherein the fluorine-substituted carbonate compound is contained in an amount of 1 to 40% by weight based on the total amount of the electrolytic solution.
The method of claim 1,
Wherein the organic solvent includes EC / EMC / DMC.
The method of claim 1,
Wherein the electrolyte has a viscosity of 100 cP or less.
11. The method of claim 10,
Wherein the electrolytic solution has a viscosity of 3 to 100 cP.
11. The method of claim 10,
Wherein the electrolytic solution has a viscosity of 3 to 15 cP.
The method of claim 1,
Wherein the electrolyte has an ion conductivity of 1.0 x 10 ^-3 to 9.9 x 10 ^-3 S / cm.
An anode including a cathode active material,
A negative electrode including a negative electrode active material, and
The electrolytic solution according to any one of claims 1 to 13
&Lt; / RTI &gt;
The method of claim 14,
And a passivation film formed on the surface of the cathode,
Wherein the passivation film is formed from the electrolyte solution.

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